1. Field of Invention
This invention relates to conduits for fluids, in general, and, more particularly, to a conduit which has a variably positioned restricting member therein for automatically providing a constant flow (volume) of fluid through the valve despite variations in inlet pressure.
2. Prior Art
In the field of fluid flow, and particularly in the field of heating and ventilating, including air-conditioning, it is desirable to provide a constant volume of fluid flow through various ducts and the like regardless of upstream (inlet) pressure variation in the supply fluid. The constant volume of fluid flow is highly desirable in order to produce even heating and/or cooling in large heating and ventilation systems.
To provide a constant volume of fluid flow, a valve which senses the upstream pressure variations and which, in response to such variations, automatically changes the cross-sectional area of the valve to compensate for the aforesaid upstream pressure variations is required. However, it is highly desirable to provide such a valve as inexpensively as possible in order to permit the system to be acceptable on a cost basis. There are known devices which function as flow control valves. However, many of the known devices have various shortcomings or problems. For example, in the known prior art type devices of similar import, constant flow is not accurately provided for various reasons. For example, in some of the existing devices back pressures, oscillations, eddy currents or the like are produced. Other devices produce a chattering or other undesirable noise effect. In addition, some of the known devices are extraordinarily expensive or require separate controls (e.g., springs) in order to vary the constant volume setting of the device. That is, most of the known devices of the type described herein have only moderate types or ranges of control and/or operation. Consequently, the devices are relatively ineffective over a broad range of flows or large pressure variations such that extensive manual adjustment and spring replacement is required in order to change flow rate. Also, these known valves tend to be inaccurate at low pressures. On the other hand, extensive manual adjustment and spring replacement in the known devices is required. Each of these approaches is terribly expensive and not very attractive to most users of this type of equipment.
Consequently, it is highly desirable to produce a valve which is capable of providing constant fluid flow over a wide range of pressure variations which can be adjusted in flow by simple manual or automatic means and to do so in a relatively inexpensive fashion.